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25 Terrestrial Laser Scanning Data Integration in Surveying Engineering Bahadır Ergün (PhD.) Gebze Institute of Technology, Geodesy & Photogrammetry Department Turkey 1. Introduction In terms of sensitivity and equipment, there are several differences between Close Range Photogrammetry (CRP) which is today often used for documentation of historical and cultural structures, restoration, relievo studies, and Terrestrial Laser Scanner (TLS) technology which is recently started to be used for 3D modelling of every kind of objects and geometric data acquisition. Terrestrial laser scanning is a new technology that enables easy and fast data acquisition from objects with complex structures such as buildings, machines, etc. In recent years, some manufacturers designed and improved different systems for specific purposes [4]. The combination of terrestrial image photogrammetry and CRP method, which is also a new technology, provides us new opportunities in presentation of 3D photorealistic models, classification of real objects and creation of visual reality [9]. TLSs usage becomes more popular day by day since they present quick and effective solutions in the way of acquiring 3D geometric information on objects. Some of the significant study areas that benefit from TLS are as follows: • Archeology, • Architectural restoration studies, • Measurement of tunnels and roads, • Urban modeling, • Virtual factories, applications of virtual reality, • Mining and infrastructure projects, • Manufacturing controls, • Crime scene investigations, • Studies of industrial design, etc. We can consider CRP and TLS as either independent methods or two complementary methods; therefore their area of application broadens day by day. If TLS and CRP are compared with Laser Scanners; • 3 dimensional points can be acquired directly • Intense point cloud data can be obtained within the frequency of millimeters, in a short period • Smooth data acquisition over difficult surfaces in terms of their form
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Laser Scanning, Theory and Applications
• Opportunity of real image acquisition If TLS and CRP are compared with Close Range Photogrammetry; • High resolution • Low costs • Since data acquisition is possible via limning, little time are the main elements and characteristics. Terrestrial laser scanners allow the imaging of the object as a point cloud by scanning them as point series in horizontal and vertical directions, under a specific angle. Point cloud data contains polar coordinates (X, Y, Z) which are based on the scanner and a value of reflection density (tons) information for each point measured. These values (polar coordinate, etc.) can be printed in several formats, namely in txt format [10].
Fig. 1.1. Sample Point Cloud Data from TLS Integration of scanning data from different station points in a single coordinate system is realized by the help of artificial targets. By coordinating the targets in question by the help of geodesic methods (Total Station etc.) object coordinates are obtained within the desired reference system. TLS point cloud data is a very intense data set, and making a study with CAD (Microstation, Autocad, etc.) software necessitates computers with very potent hardware and very experienced operators. In order the TLS data to be used in terrestrial photogrammetry, points with known coordinates that will be used in image rectification should be picked up from the whole TLS point cloud data. The sample point cloud data from TLS was shown in Fig. 1.1. The purpose of this chapter is to provide a filter creation in which surfaces in architectural photogrammetry can be automatically distinguished, so the operator's duty will be reduced under the density of point cloud taken from the surfaces via terrestrial laser scanner. Purpose of the algorithm is to obtain real surface of the scanned object and to reduce the volume of data. In this algorithm, vertical flat surfaces of the structure are auto-selected, irrelevant points are filtered. Depending on the object’s surface, different methods should be
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Terrestrial Laser Scanning Data Integration in Surveying Engineering
performed. These methods are Intersection of Plane Surfaces, Hough Transformation and a new technology based on surface projection etc. With the improvement of application areas and the advantages mentioned, terrestrial laser technology is academically an interesting topic and continues to be studied.
2. Equipment and data structure of terrestrial laser scanners Laser technology is an area of research since 1960’s; however using laser technology for the sake of making measurements is relatively new concept. As laser scanning systems are innovated, they gain a broader area of application, too. By different companies, depending on their application specifications IQSun, Leica, Optech, Callidus, Trimbe, Riegl, etc. (Table 2.1) and depending on their distance lengths (1m – 1500m) some terrestrial laser scanners which are shown in Fig. 2.1, are manufactured.
Leica -HDS 3000
Trimble- (Mensi) GS200
Leica -HDS 4500
Optech -ILRIS 3D
Riegl LMS-Z210i
Callidus -CP 3200
Fig. 2.1. Terrestrial Laser Scanners of Various Companies Specifications of several laser scanners currently used are shown in Table 2.1 with respect to their measurement distances and scanning sensitivities. According to this table, TLS system’s (Leica HDS 3000) point position accuracy can be acquired [19-23].
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Laser Scanning, Theory and Applications
Type
Measurement Range(m)
Meas. Point
Scan Station
300m (90% Reflection)
4000 point/sec.
HDS3000
300m (90% Reflection)
4000 point/sec.
HDS4500
53.5 m
500000 point/sec.
HDS6000
79 m (80% Reflection)
500000 point/sec.
3m–1500m (80% Reflection)
2500 point/sec.
LMSZ420
2m-1000m (80% Reflection)
LMSZ390
LMSZ210
Scanning Angle
2700 (V ) 0
360 ( H ) 2700 (V ) 0
360 ( H )
Distance Accuracy
Position Accuracy
Light Beam
4 mm @ 50 m
6 mm @ 50 m
4 mm @ 50 m
4 mm @ 50 m
6 mm @ 50 m
4 mm @ 50 m
5mm+120pp 13.7mm m @ 25 m (%100yns. y.)
8.5 mm @ 25 m
Leica
Optech Ilris 3D
Riegl
Z–F
Faro
Imager 5006
LS 880
3100 (V ) 0
360 ( H ) 3100 (V )
5 mm @ 50 m
10 mm 3 mm + @ 50 m 0.22mrad
7 mm @ 100 m
8 mm 0 @ 100 m 0.00974
0 − 80 0 (V ) 12000 point/sec. 0 − 3600 ( H )
8 mm @ 50 m
10 mm @ 50 m
0.25 mrad
1m-300m (80% Reflection)
0 − 80 0 (V ) 11000 point/sec. 0 − 3600 ( H )
4 mm @ 50 m
6 mm @ 50 m
0.25 mrad
4m-650m (80% Reflection)
0 − 80 0 (V ) 12000 point/sec. 0 − 3600 ( H )
10 mm @ 50 m
15 mm @ 50 m
2.7 mrad
1m – 79 m
500000 point/sec.
mm @ 50 m
1 mm @ 50 m
0.22 mrad
1 m – 80 m
12000 point/sec.
3 mm
5 mm
0.010
0
360 ( H ) 3100 (V ) 0
360 ( H )
3100 (V ) 0
360 ( H ) 3200 (V ) 3600 ( H )
Table 2.1. Laser Scanners and Their Specifications
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Terrestrial Laser Scanning Data Integration in Surveying Engineering
2.1 Equipment structure of terrestrial laser scanners In this section, a Terrestrial Laser Scanner is used and as it is figured out in Fig. 2.2, the components of a Terrestrial Laser Scanner are: • Scanner, • Control unit, • Power source, • Stand
Fig. 2.2. Terrestrial Laser Scanner Used In This Application and Its Components Scanning unit is the part that obtains 3D data in TLS system. They can be examined under three groups depending on their distance measuring method. Measurement Model Flight Time Phase Diff. Optical Trian.
Range (m)
Accuracy (mm)